This invention relates to a semiconductor integrated circuit device and a manufacturing technique therefore; and more particularly, the invention relates to a technique effective for use in a semiconductor integrated circuit device, provided with a protection circuit having a thyristor structure, and a manufacturing technique therefore.
With advances in miniature processing technology in a semiconductor manufacturing process, miniaturization of elements, interconnections, etc. constituting a semiconductor integrated circuit device, is now receiving considerable attention. With such miniaturization, the performance of the semiconductor integrated circuit device is increasingly improving.
On the one hand, however, a problem arises in that the miniaturized elements, interconnections, etc. are extremely susceptible to an excessive voltage or overvoltage, such as static electricity or the like, and are easily broken. There has been a strong demand for elucidation of the mechanism which causes the deterioration and the destructive phenomena due to static electricity and the establishment of a protective structure with a view toward ensuring the reliability of the semiconductor integrated circuit device.
Meanwhile, the present inventors have discussed a protection circuit having a thyristor structure. This protection circuit is electrically connected to a wiring path for connecting an external terminal and an internal circuit to one another. Described more specifically, the protection circuit is constructed by electrically connecting, for example, a thyristor having p+, n, p and n+ between an external terminal and a ground potential.
In the present protection circuit, a discharge path varies according to the polarity of the voltage applied from the outside. The protection circuit has a structure wherein, when an excessive voltage or overvoltage applied from the outside is positive, the protection circuit is discharged in accordance with the operation of the thyristor; and, when the overvoltage is negative, it is discharged in accordance with the operation of each lateral bipolar transistor.
A known protection circuit has been described in, for example, the IEEE, 1991, CUSTOM INTEGRATED CIRCUIT CONFERENCE 27.2.1. According to this reference, since parasitic bipolar transistors, each having a large drive capability, are used as protection elements, a surge current is allowed to escape satisfactorily so that the electro static discharge (hereinafter called xe2x80x9cESDxe2x80x9d) resistance can be enhanced.
Further, a protection circuit having a thyristor structure has been described in, for example, the 1988 EOS/ESD SYMPOSIUM PROCEEDINGS [A PROCESS-TOLERANT INPUT PROTECTION CIRCUIT FOR ADVANCED CMOS PROCESSES], P201-P205. The basic device structure and operation of a thyristor constituting the protection circuit have been explained in this publication.
Another known protection circuit having a thyristor structure has been disclosed in, for example, Japanese Patent Application Laid-Open No. 4-196352 (reference 1) or Japanese Patent Application Laid-Open No. 6-62529 (reference 2). According to these references 1 and 2, a diode (corresponding to reference numeral 300 in FIG. 3 or the like in the reference 1 or symbol D1 in FIG. 1 or the like in the reference 2) for the protection circuit is provided in a stage posterior to a thyristor for the protection circuit. In these references, however, the diode is provided in a stage posterior to a resistor for the protection circuit, which has been intentionally added to the stage posterior to the thyristor, and is provided in a region different from a well in which the thyristor is provided in a semiconductor substrate.
However, the present inventors have discovered a problem in the protection circuit having a thyristor structure in that a difference in the ESD resistance tends to occur according to the polarity of an overvoltage applied from the outside.
That is, the protection circuit having a thyristor structure has a problem in that, when the holding voltage is low and the amount of energy used up or consumed through the discharge path is dispersed in a low state when the discharge is carried out through the thyristor (when a positive overvoltage is applied), the ESD resistance is high; whereas when the holding voltage is high, the amount of energy consumed through the discharge path is large and the discharge current is easily concentrated on a reverse junction when the discharge is carried out through each lateral bipolar transistor (when a negative overvoltage is applied), the ESD resistance is low.
Therefore, an object of the present invention is to provide a technique which is capable of eliminating the difference in ESD resistance caused by different polarities of overvoltages applied to an external terminal, and which is capable of enhancing the ESD resistance of a semiconductor integrated circuit device to both positive and negative overvoltages.
The above and other objects and novel features of the present invention will become apparent from the description provided in the present specification and the accompanying drawings.
A summary of typical features of the invention as disclosed in the present application will be described in brief in the following manner.
According to one aspect of the present invention, there is provided a semiconductor integrated circuit device comprising:
a protection element having a thyristor structure, which is electrically connected between an external terminal and a ground potential, the protection element being provided on a semiconductor substrate, and
a diode serving as a protection element electrically connected between the external terminal and the ground potential so that the diode is connected in the forward direction when a negative overvoltage is applied to the external terminal.
Thus, since a diode for allowing a negative overvoltage to escape is provided as a protection element as well as a thyristor for allowing a positive overvoltage to escape, an excessive current or overcurrent is allowed to promptly escape from a ground potential to an external terminal through the diode when the negative overvoltage is applied to the external terminal. It is therefore possible to enhance the ESD resistance to a negative overvoltage. That is, according to the present invention, since a high ESD resistance to both positive and negative overvoltages applied to the external terminal can be obtained, the yield and reliability of the semiconductor integrated circuit device can be enhanced.
Further, since a protection circuit element is made up of a diode of relatively small area, the entire occupied area of a protection circuit will not significantly increase. Therefore, a high ESD resistance to both positive and negative overvoltages applied to the external terminal can be obtained.
According to another aspect of the present invention, there is provided a semiconductor integrated circuit device, wherein a protection element having the thyristor structure includes;
a first semiconductor region of a conductivity type opposite to that of the semiconductor substrate, which is formed in an upper layer of the semiconductor substrate;
a second semiconductor region of a conductivity type opposite to that of the semiconductor substrate, the second semiconductor region being formed in an upper layer of the semiconductor substrate so as to be spaced away from the first semiconductor region;
a third semiconductor region corresponding to a region of a conductivity type opposite to that of the first semiconductor region, the third semiconductor region being formed between at least the first semiconductor region and the second semiconductor region in the semiconductor substrate;
a fourth semiconductor region formed within the first semiconductor region, constructed by a semiconductor region of the same conductivity type as that of the first semiconductor region and electrically connected to the external terminal;
a fifth semiconductor region formed within the first semiconductor region so as to be adjacent to the fourth semiconductor region, constructed by a semiconductor region of a conductivity type opposite to that of the first semiconductor region and which is electrically connected to the external terminal;
a sixth semiconductor region of the same conductivity type as that of the first semiconductor region, the sixth semiconductor region having one portion disposed in the first semiconductor region and the other portion disposed in a region between the first semiconductor region and the second semiconductor region; and
a seventh semiconductor region having one portion disposed in the second semiconductor region and the other portion disposed in a region between the first semiconductor region and the second semiconductor region so as to be spaced away from the sixth semiconductor region, the seventh semiconductor region being constructed by a semiconductor region of the same conductivity type as that of the first semiconductor region and being electrically connected to the ground potential; and
a diode having an eighth semiconductor region of a conductivity type opposite to that of the first semiconductor region, the eighth semiconductor region being electrically connected to the ground potential and provided within the first semiconductor region.
Thus, since the resistance of a discharge path for an overcurrent can be reduced, the overcurrent is allowed to escape promptly.
According to a further aspect of the present invention, there is provided a semiconductor integrated circuit device wherein the fourth semiconductor region and the eighth semiconductor region are disposed so that respective long sides thereof are opposed to each other in parallel. Thus, the width of a discharge path for an overcurrent can be broadened and the discharge path can be reduced in resistance. Therefore, the overcurrent is allowed to escape rapidly owing to the reduction in the discharge path resistance.
According to a still further aspect of the present invention, there is provided a method of manufacturing a semiconductor integrated circuit device, comprising the step of simultaneously carrying out impurity introducing steps for forming the fifth semiconductor region constituting the protection element having a thyristor structure and the eighth semiconductor region constituting the protection element formed by the diode with the same photoresist patterns as masks in a manufacturing process of the semiconductor integrated circuit device.
Thus, since the manufacturing process of the semiconductor integrated circuit device can be simplified, a reduction in manufacturing time of the semiconductor integrated circuit device and a decrease in manufacturing cost thereof can be promoted.
According to a still further aspect of the present invention there is provided a semiconductor integrated circuit device comprising:
a signal external terminal for externally inputting a signal;
a reference potential external terminal externally supplied with a reference potential;
a protection element having a thyristor structure;
a protection element having a diode structure;
the signal external terminal, the reference potential external terminal, the protection element having the thyristor structure and the protection element having the diode structure being provided on a semiconductor substrate; and
a protection circuit structure wherein the protection element having the thyristor structure and the protection element having the diode structure are connected in parallel between the signal external terminal and the reference potential external terminal,
the protection element having thyristor structure including;
a first semiconductor region of a first conductivity type, which is formed in the semiconductor substrate;
a second semiconductor region of said first conductivity type, which is formed in the semiconductor substrate at a position spaced away from the first semiconductor region;
a third semiconductor region of a second conductivity type, the third semiconductor region corresponding to a region of a conductivity type opposite to that of the first conductivity type and being formed between at least the first conductivity type first semiconductor region and the first conductivity type second semiconductor region in the semiconductor substrate;
a fourth semiconductor region of said first conductivity type, which is formed within the first conductivity type first semiconductor region and is electrically connected to the signal external terminal;
a fifth semiconductor region of said second conductivity type, which is formed within the first conductivity type first semiconductor region and is electrically connected to the signal external terminal;
a sixth semiconductor region of said first conductivity type, the sixth semiconductor region being formed in the semiconductor substrate so that a portion thereof is disposed in the first conductivity type first semiconductor region and the second conductivity type third semiconductor region; and
a seventh semiconductor region of said first conductivity type, which is formed in the semiconductor substrate so that a portion thereof is disposed in the first conductivity type second semiconductor region and the second conductivity type third semiconductor region, the seventh semiconductor region being electrically connected to the reference potential external terminal; and
the protection element having a diode structure including:
an eighth semiconductor region of said second conductivity type, which is formed within the first conductivity type first semiconductor region and is electrically connected to the reference potential external terminal.
According to a still further aspect of the present invention, there is provided a semiconductor integrated circuit device comprising:
a semiconductor substrate;
an MIS transistor formed in the semiconductor substrate and having a gate, a source and a drain;
a signal external terminal formed in the semiconductor substrate and which is electrically connected to the gate of the MIS transistor to input an externally-supplied signal to the gate of the MIS transistor;
a reference potential external terminal formed in the semiconductor substrate and which is electrically connected to the source of the MIS transistor to supply an externally-input reference potential to the source of the MIS transistor;
a protection element having a thyristor structure, which is formed in the semiconductor substrate and is electrically connected between the signal external terminal and the reference potential external terminal;
a protection element having a diode structure, which is formed in the semiconductor substrate and is electrically connected between the signal external terminal and the reference potential external terminal; and
a protection element provided at the semiconductor substrate, the protection element being provided between both the protection element having the thyristor, structure and the protection element having the diode structure and the gate of the MIS transistor, being electrically connected between the signal external terminal and the reference potential external terminal, and serving so as to reduce the difference in potential between the source and gate of the MIS transistor when a voltage greater than that used upon normal operation thereof is applied to the MIS transistor.
According to a still further aspect of the present invention, there is provided a semiconductor integrated circuit device comprising:
a signal external terminal for externally inputting a signal;
a reference potential external terminal externally supplied with a reference potential;
an MIS transistor having a source, a drain and a gate, the gate being electrically connected to the signal external terminal and the source being electrically connected to the reference potential external terminal;
a protection element having a thyristor structure; and
a protection element having a diode structure;
the signal external terminal, the reference potential external terminal, the MIS transistor, the protection element having the thyristor structure and the protection element having the diode structure being provided on a semiconductor substrate; and
wherein the protection element having the thyristor structure and the protection element having the diode structure are connected in parallel between the signal external terminal and the reference potential external terminal;
the protection element haying the thyristor structure including:
a first semiconductor region of a first conductivity type, which is formed in the semiconductor substrate;
a second semiconductor region of said first conductivity type, which is formed in the semiconductor substrate at a position spaced away from the first semiconductor region;
a third semiconductor region of a second conductivity type, the third semiconductor region corresponding to a region of a conductivity type opposite to the first conductivity type and being formed between at least the first conductivity type first semiconductor region and the first conductivity type second semiconductor region the semiconductor substrate;
a fourth semiconductor region of said first conductivity type formed within the first conductive type first semiconductor region and electrically connected to the signal external terminal;
a fifth semiconductor region of said second conductivity type formed within the first conductive type first semiconductor region and electrically connected to the signal external terminal;
a sixth semiconductor region of said first conductivity type, the sixth semiconductor region being formed in the semiconductor substrate so that a portion thereof is disposed in the first conductivity type first semiconductor region and the second conductivity type third semiconductor region; and
a seventh semiconductor region of said first conductivity type, which is formed in the semiconductor substrate so that a portion thereof is disposed in the first conductivity type second semiconductor region and the second conductivity type third semiconductor region, the seventh semiconductor region being electrically connected to the reference potential external terminal; and
the protection element having the diode structure including;
an eighth semiconductor region of said second conductivity type, which is formed within the first conductivity type first semiconductor region and is electrically connected to the reference potential external terminal.